This is the first application filed for the present invention.
This invention relates to digital printing and particularly to a method and apparatus for separating, rasterizing and distributing data for high-speed digital printing.
Advances in ink-jet module technology have enabled the high-speed printing of continuously varying images containing a mixture of text of different fonts and image files of various formats. For example, applicant has developed ink-jet modules that permit full-color (such as cyan, magenta, yellow, and black (CMYK)), high resolution (360 dots per inch (dpi)), and full page width (11.33 inches) images to be printed at high speed, as is explained in co-pending U.S. Patent Application Serial No. 10/366,514 entitled xe2x80x9cAPPARATUS FOR ALIGNMENT OF MULTIPLE PAGE-WIDE ARRAY PRINT HEADSxe2x80x9d, which is incorporated herein by reference. However, a problem arises in processing image data at rates required to sustain the high speed printing. For example a steady bit rate of about 3.84 Gbps is required for dual-sided 4-color printing of 360 dpi.
Using the fastest available computers, processing of heterogeneous image data at this rate is not possible in most of today""s affordable computers. While some mainframe computers may be able to provide this processing the expense of such computers is considerable. There therefore exists a need for an apparatus and method for processing electronic image data to ink-jet modules to enable high-speed printing.
It is an object of the invention to provide a printer and a method for processing image data to ink-jet modules for high-speed printing.
Accordingly, a printing apparatus is provided for printing an image on a printable material. The printing apparatus includes a computer for receiving image data in a format for printing, and preflighting the image data to limit a computational complexity of raster image processing (ripping) required to convert the image data to a bitmap image. A printer processor in communications with the computer is adapted to separate the image data into a plurality of monochrome image data sets and distributing the monochrome image data sets to respective print heads of the printing apparatus. Each of the print heads includes a raster image processor for ripping the monochrome image data sets to form bitmap image data sets. As each print head processor only rips a respective monochrome image, and the computational complexity of the monochrome image data set is bounded by the preflighting, data of variable content can be reliably received at the ink jet modules in a timely manner.
The preflighting may use software for detecting any of the following potential problems: a missing font; a broken link; a color out of bounds of a predetermined color palette; an extraneous element; incorrect trapping; incorrect bleeds; and a number fonts having resolutions that differ from that of the print heads in a page in excess of an empirically derived threshold. If a potential problem is detected, the preflight software applies an associated remedial procedure to the image data. Preferably, if an excessive number of fonts having differing resolutions are detected, the associated step of applying remedial procedures comprises a step of renormalizing the resolutions of the fonts to reduce computational complexity of ripping.
Each of the print heads preferably further comprises a plurality of ink-jet modules arranged in at least first and second staggered rows to provide an evenly spaced collection of print lines across a width of the printable material. Each of the first and second rows may comprise complementary pairs of ink-jet modules that are spaced apart in a direction of travel of the printable material, the complementary pairs of the ink-jet modules in the respective rows, the modules in each of the complementary pairs being offset from each other by one-half of a dot spacing of the ink-jet modules in a direction perpendicular to the motion of the printable material within the plane of the printable material, in order to double the print resolution of the printer. Analogous arrangements of multiple rows providing for higher resolutions are possible.
Preferably each of the print heads further comprises a print-strip data distributor for dividing the bitmap image data into a plurality of print-strip data sets that correspond to respective print areas printed by respective ones of the complementary pairs of ink-jet modules. Dot distributors may therefore be required for receiving respective ones of the print-strip data sets, separating the respective print-strip data sets into odd dot data and even dot data, and sending the respective odd dot data set and even dot data set to associated ink-jet modules of the respective pairs of print heads.
In accordance with one embodiment of the invention, the raster image processor, print-strip distributor and dot distributors of each of the print heads can be embodied by a special purpose computer.
The printing apparatus may include a first plurality of print heads for printing a first side of the printable material and a second plurality of print heads for printing a second side of the printable material.
Preferably the printable material is a continuous web, and the printing apparatus further comprises feed mechanisms for moving the continuous web past the first and second plurality of print heads. The printing apparatus may further comprise a cutter for cutting the continuous web into printed sheets, and may further include a stacker for stacking the printed sheets.
A method for processing color image data for high-speed digital printing is also provided. The method involves receiving preflighted image data from a computer print manager, separating image data into a plurality of monochrome image data sets, and distributing the monochrome image data sets to respective print heads. At the print heads, the monochrome image data sets are ripped to form bitmap image data sets, that are used to drive ink-jet modules to print the monochrome color image at each print head so that the monochrome color images are seamlessly overlaid to form the desired image.